The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.) define a way wireless local area networks (WLANs) must work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium Access Control) operating mode implements the well-known Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the so-called “Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA) technique.
More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11ax task group, as the successor of 802.11ac. The primary goal of the 802.11ax task group consists in seeking for an improvement in data speed to wireless communicating devices used in dense deployment scenarios.
In this context, multi-user (MU) transmission has been considered to allow multiple simultaneous transmissions to/from different users in both downlink (DL) and uplink (UL) directions from/to the AP and during a transmission opportunity granted to the AP. In the uplink, multi-user transmissions can be used to mitigate the collision probability by allowing multiple non-AP stations to simultaneously transmit. To actually perform such multi-user transmission, it has been proposed to split a granted communication channel into sub-channels, also referred to as resource units (RUs), that are shared in the frequency domain by multiple users (non-AP stations/nodes), based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique.
A 802.11ax node has thus the opportunity to gain access to the medium via two access schemes: MU UL access scheme and conventional EDCA (Enhanced Distributed Channel Access) contention-based access scheme. To keep access to the medium fair between the 802.11ax nodes and the legacy nodes, solutions have been proposed to modify, upon successfully transmitting data over an accessed resource unit (i.e. through UL OFDMA transmission), a current value of at least one queue contention parameter into a penalized or degraded value, to reduce a probability for the node to access a communication channel through (EDCA) contention. For instance, the penalized or degraded value is more restrictive than the original (or legacy) value.
Proposed solutions for restoring fairness between 802.11ax nodes and legacy nodes introduce however some complexity for managing the Quality-of-Service (QoS) at a 802.11ax node. For example, strongly penalizing the EDCA medium access when using MU UL may result in that some traffic that cannot be sent using the Multi User Uplink scheme is then strongly penalized and even purely discarded. In this situation the QoS provided by the WLAN is deteriorated and the performance of the application relying on the MAC layer is degraded.